Balancing devices of the known type provide for dynamic measurement of the imbalance of a rotating element mounted in its own receptacle, complete with bearings, and turned at the service rate. The rotating element can be for example a wheel or a rotor.
The normal balancing method requires measuring the vibrations at one or more rotation rates in a certain measurement range, for example between 20,000 rpm and 200,000 rpm.
Known balancing machines of the “supercritical” or “soft bearing” type provide said measurement of the vibrations by turning the rotating element in what are called supercritical conditions, i.e., so that the resonance frequencies generated by the elastic elements that support the support complete with the rotating element and its receptacle are substantially lower than the vibration measurement range.
In balancing machines of the known type, the rotating element, complete with its receptacle that supports the bearings, is mounted on a support that is connected to the base structure of the machine in a relatively elastic manner, so as to ensure a resonance in all its vibration modes outside the speed of use of the system under the selected measurement conditions. Vibration measurement is performed generally by means of a sensor, for example an accelerometer, which is fixed to the vibrating part of the balancing machine The extent of the measured vibration, with equal actual imbalances of the rotating element, depends on the mass and on the moment of inertia of the vibrating part of the balancing machine
It follows that a drawback of balancing machines of the known type relates to the fact that this mass is often substantial, and this entails the considerable reduction of the measured value of the vibrations.
In particular, in known balancing devices the fixing of the receptacle and of the rotating element to the corresponding supporting structure is a very critical aspect for good vibration measurement. Very rigid fixing is in fact indispensable in order to prevent the rotating element and its receptacle from deforming or detaching from the supporting structure due to the dynamic forces in play, causing unwanted resonances or non-linearities of vibration measurement.
Currently, various techniques and various devices are known for fixing a rotating element and corresponding receptacle to a balancing device and will be described hereinafter together with the related drawbacks.
It is known, for example, to fasten the receptacle of the rotating element to the corresponding supporting structure by means of bolts. However, a drawback of this solution relates to the time required to perform, manually, the fixing operation; the long time required to perform fixing is in fact not compatible with the production times of the facilities in which balancing machines operate.
Solutions for fixing the receptacle of the rotating element are also known which use hydraulic actuators, or actuators of another type, capable of providing well-controlled fixing forces to the supporting structure, and in a direction that is parallel to the rotation axis of the rotating element. However, these actuators have the drawback of being bulky and of having a considerable mass, and since they are mounted on the vibrating part of the balancing machine they entail the considerable and undesirable increase of the oscillating mass. The increase of the oscillating mass is a very undesirable drawback, because it entails the modification of the vibration mode of the vibrating part on which the vibrations caused by the rotating element are measured. In particular, the increase in mass causes a sharp reduction in the measured vibration, reducing therefore the sensitivity of the measurement system. Moreover, the addition of mechanical components on the vibrating part increases the likelihood of adding vibrating modes in the range of useful frequencies of the measurement, introducing new resonances that are harmful for the quality of the measurement.
Radial cylindrical actuators are also known which are opposite to the receptacle of the rotating element and bear simple V-shaped blocks that fasten the supporting structure, for example a supporting ring, to the receptacle of the rotating element. However, this known fixing system has the drawback that it can be used only for some appropriate shapes of the fixing part of the receptacle. Another drawback resides in that this system cannot provide a known and controllable axial fastening force, due to the friction inside the V-shaped block itself, which is pressed only radially.